The brain dead answer is Nitto. Their stems are as nice as you want to pay for. The top end, the Pearl, is as nice (and probably better machined, accurate, etc.) as any stem made. Most of Nitto's stems are measured like everybody else's. but note: the Pearl is measured handlebar center to intersection of stem centerline and steerer centerlinr. So, take the Pearl named dimension and multiply by 1.08. (A Pearl 12 is a Cinelli/TTT 130.)

Google Nitto Pearl. It doesn't look like yours; more like an older Cinelli. Web photos do not do it justice. In your hands it is a knockout. Especially when you can see all the machining detail normally hidden by bar and steerer. In production and probably will be for a while. They come both 25.4 and 26.0 mm dia.

Ben